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Oxidation of melatonin by carbonate radicals and chemiluminescence emitted during pyrrole ring cleavage
Author(s) -
Hardeland Rüdiger,
Poeggeler Burkhard,
Niebergall Robert,
Zelosko Veronika
Publication year - 2003
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1034/j.1600-079x.2003.02941.x
Subject(s) - chemistry , radical , chemiluminescence , photochemistry , tiron , hemin , hydrogen peroxide , melatonin , hydroxyl radical , superoxide , catalysis , peroxide , carbonate , organic chemistry , medicine , heme , enzyme
Oxidation of melatonin was followed by measuring chemiluminescence emitted during pyrrole ring cleavage, a process leading to the main oxidation product of this indoleamine, N 1 ‐acetyl‐ N 2 ‐formyl‐5‐methoxykynuramine (AFMK). Radical reactions of melatonin were studied in two variants of a moderately alkaline (pH 8) H 2 O 2 system, one of which contained hemin as a catalyst. In both systems, light emission from melatonin oxidation lasted several hours. Time courses and turnover rates depended on the presence or absence of hemin; the catalyst enhanced light emission many‐fold. In the two reaction systems, the presence of hydrogen carbonate (HCO) enhanced chemiluminescence by more than 10‐fold, indicating scavenging of carbonate radicals. In the presence of 10% dimethylsulfoxide (DMSO) or 1 m mannitol, HCO‐dependent as well as independent light emissions were only partially inhibited. With regard to the stimulatory effect of HCO, this implies a formation of carbonate radicals () independent of hydroxyl ( ḃ OH) radicals, presumably involving superoxide anions abundantly present in the system. Tiron, a scavenger of superoxide anions, strongly and almost instantaneously inhibited chemiluminescence, in accordance to the requirement of this reactive oxygen species for AFMK formation and its involvement in ‐radical formation. Melatonin's capability of scavenging CO may contribute to its protective potency.